Conventional communication systems in which a piece of communication apparatus provided with an interference canceller is used are shown as follows. FIG. 1 is a view showing a configuration of a piece of conventional base station apparatus provided with an interference canceller, and a system in which the above base station apparatus performs radio communication with pieces of mobile station apparatus.
FIG. 1 shows that a piece of mobile station apparatus (A) 1601 and that of (B) 1602 perform radio communication with a piece of base station apparatus 1607. Here, the mobile station apparatus (A) 1601, and that of (B) 1602 use wireless channels 1603, 1604 and those 1605, 1606, respectively, for communication with the base station apparatus 1607. All the above wireless channels use the same frequency. Hereinafter, an uplink and a downlink will be separately described.
In the first place, the uplink will be described. Signals transmitted from the mobile station apparatus (A) 1601, and that from (B) 1602 are received by antennas 1608, 1609 of the base station apparatus 1607.
In the base station apparatus 1607, the signals received by the antennas 1608, 1609 are demodulated by radio processing sections 1610, 1611, respectively. In a channel estimation section 1612, the states of the wireless channels 1603 through 1606 are estimated using the demodulated signals.
In an interference canceller 1613, a received signal 1614 of the mobile station apparatus (A) and a received signal 1615 of the mobile station apparatus (B) after cancellation of the mutual interference are obtained using the demodulation signals from the radio processing section 1610, and that from the radio processing section 1611, respectively, based on the estimation results by the channel estimation section 1612.
Thereby, though both of a transmission signal of the mobile station apparatus (A) and that of (B) are carried in the same frequency, the received signals 1614, 1615 with cancelled interference are obtained in the base station 1607. Therefore; improved frequency efficiency may be obtained for the uplink, as signals of a plurality of users are multiplexed in the same frequency.
Then, the downlink will be described. In the base station apparatus 1607, a transmission signal 1616 to the mobile station apparatus (A), and a transmission signal 1617 to the mobile station apparatus (B) are modulated by radio processing sections 1618, 1619, respectively. The signals modulated by the radio processing sections 1618 and that by 1619 are transmitted through the antennas 1608, 1609.
In the mobile station apparatus (A) and that of (B), a signal mixing the transmission signals 1616, 1617 transmitted from the base station apparatus is received. Then, desired signals maybe separated from a signal mixing signals of a plurality of users by provision of a similar interference canceller to that of the base station apparatus 1607 even in the mobile station apparatus (A) and that of (B). Thereby, improved frequency efficiency may be also obtained for the downlink, as signals of a plurality of users are multiplexed in the same frequency.
However, pieces of communication apparatus provided with a conventional interference canceller have had the following problems. That is, the above interference canceller requires a large amount of calculations, and information (for example, unique words) on all the users using the same frequency. Therefore, there has been a problem that it is difficult to install a piece of communication apparatus provided with the above conventional interference canceller in pieces of mobile station apparatus, considering the electric power consumption, the cost, the size, the complexity of the control signals, and so on.
Moreover, pieces of communication apparatus provided with the conventional interference canceller have had a problem that the quality of received signals is deteriorated by the effects of delay waves, when there are the above delay waves in channels used, as the above pieces of communication apparatus suppress only the effect of interference.